This article investigates two questions: One, how might the very differently structured social collectives on the Internet – masses, crowds, communities and movements – be classified and distinguished? And two, what influence do the technological infrastructures in which they operate have on their formation, structure and activities? For this we differentiate between two main types of social collectives: non-organized collectives, which exhibit loosely-coupled collective behavior, and collective actors with a separate identity and strategic capability. Further, we examine the newness, or distinctive traits, of online-based collectives, which we identify as being the strong and hitherto non-existent interplay between the technological infrastructures that these collectives are embedded in and the social processes of coordination and institutionalization they must engage in in order to maintain their viability over time. Conventional patterns of social dynamics in the development and stabilization of collective action are now systematically intertwined with technology-induced processes of structuration.